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Duodenal Nitrogen Flow in Response to Increasing Dietary Crude Protein in Sheep¹

University of Wisconsin, Madison 53706

Abstract

Four reentrant cannulated yearling rams weighing approximately 50 kg were utilized in a 4 x 4 Latin square design to measure the quantity and quality of nitrogenous compounds reaching the duodenum when diets containing 8, 11, 14 of 17% crude protein were fed. One killogram of pelleted diet was fed daily in equal portions at 12-hr intervals. Soybean meal was substituted for corn to increase protein concentration. All diets were calculated to be isocaloric based on digestible energy content and to contain sufficient digestible protein such that maximum microbial protein synthesis per unit of energy available would be achieved. Thus, increases in duodenal nitrogen could be attributed to differences in apparent escape of dietary crude protein (nitrogen) from ruminal degradation. Based on estimates of diaminopimelic acid and nucleic acid nitrogen, microbial protein synthesis was not significantly different between treatments.

A linear increase (P<.05) in total nitrogen flowing to the duodenum (g/24 hr) with increasing concentration of crude protein in the diet was observed. At 1% increase in dietary crude protein (1.6 g nitrogen) resulted in an additional .51 g of nitrogen reaching the duodenum, indicating a 31.7% (standard error of beta = .18) apparent escape of dietary crude protein. Increases in individual amino acids flowing to the duodenum (g/24 hr) were generally significant. The essential to nonessential amino acid ratio increased linearly (P<.01) with increasing dietary crude protein. Ammonia nitrogen (NH³-N) increased linearly (P<.01) while duodenal nitrogen as a percentage of nitrogen intake followed a curvilinear decline (P<.01 for both linear and quadratic terms) as dietary crude protein increased.

The use of chromic oxide as an indicator of nutrient flow to the duodenum was evaluated with respect to the method of sampling from reentrant cannulae. There was significant variation in the flow of duodenal digesta (ml/24 hr) with respect to time of feeding. Flow of chromic oxide to the duodenum was not closely associated with flow of nitrogen to the duodenum as indicated by variation (P<.01) in the nitrogen to chromic oxide ratio in duodenal digesta with respect to time of feeding.

¹ Department of Meat and Animal Science. Research was supported by the College of Agricultural and Life Sciences. This is Paper No. 715 from the Department of Meat and Animal Science.

² Present address: Department of Animal Sciences, University of Kentucky, Lexington 40506.